System and method for exhaust-gas aftertreatment of an internal combustion engine

Abstract

The invention relates to an exhaust gas aftertreatment system for a spark ignition internal combustion engine based on the Otto principle. The internal combustion engine is connected on the outlet side to an exhaust gas system, wherein an electrically heatable three-way catalytic converter, a four-way catalytic converter downstream from the electrically heatable three-way catalytic converter, and a further three-way catalytic converter downstream from the four-way catalytic converter are situated in the exhaust gas system in the flow direction of an exhaust gas through the exhaust gas system. Before the internal combustion engine is started, the electrically heatable three-way catalytic converter and preferably also the four-way catalytic converter are heated to allow efficient exhaust gas aftertreatment of the untreated emissions of the internal combustion engine upon starting the internal combustion engine. The exhaust gas aftertreatment system is also configured to allow efficient conversion of the pollutants also during a regeneration of the four-way catalytic converter, and thus, to ensure particularly low emissions in all operating states of the motor vehicle.

The invention claimed is: 
     
       1. An exhaust gas aftertreatment system for a spark ignition internal combustion engine, comprising:
 an exhaust gas system that is connected to an outlet of the internal combustion engine, 
 an electrically heatable three-way catalytic converter disposed close to the engine, downstream from the outlet, 
 a four-way catalytic converter disposed downstream from the electrically heatable three-way catalytic converter, 
 a second three-way catalytic converter disposed downstream from the four-way catalytic converter, 
 a secondary air system configured to blow secondary air into the exhaust gas system, upstream from the electrically heatable three-way catalytic converter, and 
 a burner provided in the exhaust gas system disposed downstream from the electrically heatable three-way catalytic converter and disposed upstream from the four-way catalytic converter, and configured to heat the four-way catalytic converter. 
 
     
     
       2. The exhaust gas aftertreatment system according to  claim 1 , further comprising an HC adsorber in the exhaust gas system, downstream from the electrically heatable three-way catalytic converter and upstream from the four-way catalytic converter. 
     
     
       3. The exhaust gas aftertreatment system according to  claim 1 , wherein the secondary air system includes a secondary air pump configured to supply the burner with fresh air and a secondary air valve, the secondary air valve being situated on an outlet side on a cylinder head of the internal combustion engine. 
     
     
       4. The exhaust gas aftertreatment system according to  claim 3 , wherein the secondary air pump is connected to the burner via the second secondary air line and a second secondary air valve. 
     
     
       5. The exhaust gas aftertreatment system according to  claim 2 , further comprising:
 a first temperature sensor disposed downstream from an opening of the burner into an exhaust duct of the exhaust gas system and upstream from the four-way catalytic converter, and 
 a second temperature sensor disposed downstream from the four-way catalytic converter. 
 
     
     
       6. The exhaust gas aftertreatment system according to  claim 1 , further comprising lambda sensors situated in the exhaust duct, in each case upstream and downstream from the electrically heatable three-way catalytic converter and upstream and downstream from the four-way catalytic converter, the lambda sensors being designed as hydrolock-resistant, electrically heatable lambda sensors. 
     
     
       7. A method for exhaust gas aftertreatment of an internal combustion engine, having an exhaust gas aftertreatment system comprising:
 an exhaust gas system connected to an outlet of the internal combustion engine, 
 an electrically heatable three-way catalytic converter disposed close to the engine downstream from the outlet, 
 a four-way catalytic converter disposed downstream from the electrically heatable three-way catalytic converter, 
 a second three-way catalytic converter disposed downstream from the four-way catalytic converter, 
 a secondary air system capable of blowing secondary air into the exhaust gas system upstream from the electrically heatable three-way catalytic converter, and 
 a burner provided in the exhaust gas system downstream from the electrically heatable three-way catalytic converter and upstream from the four-way catalytic converter and being configured to heat the four-way catalytic converter, the method comprising: 
 prior to or upon starting the internal combustion engine, starting to heat the electrically heatable three-way catalytic converter by a trigger signal provided by a signal generator, and 
 activating the burner to heat up the electrically heatable three-way catalytic converter and the four-way catalytic converter to a light-off temperature as quickly as possible. 
 
     
     
       8. The method for exhaust gas aftertreatment of the internal combustion engine according to  claim 7 , wherein the signal generator is a door contact switch, a sensor for seat occupancy, a receiver for a keyless locking system, a seat belt sensor, or a control unit of a hybrid vehicle.